protochlorophyllide

thumb|The Arabidopsis thaliana|Arabidopsis mutant (FLU), unable to control biosynthesis of protochlorophyllide, glows red in the blue light.

Protochlorophyllide, or monovinyl protochlorophyllide, is an intermediate in the biosynthesis of chlorophyll a. It lacks the phytol side-chain of chlorophyll and the reduced pyrrole in ring D. Protochlorophyllide is highly fluorescent; mutants that accumulate it glow red if irradiated with blue light. In angiosperms, the later steps which convert protochlorophyllide to chlorophyll are light-dependent, and such plants are pale (chlorotic) if grown in the darkness. Gymnosperms, algae, and photosynthetic bacteria have another, light-independent enzyme and grow green in the darkness as well.